1. Field of the Invention
The present invention relates to a sheet conveying apparatus. More particularly, the present invention relates to a sheet discharging apparatus as the sheet conveying apparatus, and an image forming apparatus having this sheet discharging apparatus in which a sheet having an image formed thereon is discharged by sheet discharging means and a rotary member rotated by a rotation of the sheet discharging means while the sheet is pressed by the rotary member.
2. Related Background Art
In one example of the image forming apparatus, there is conventionally known a recorder such as a printer, a copying machine, a facsimile, or a recorder used as an output device for a composite type electronic device including a computer, a word processor, etc. or a work station. Such a recorder is constructed such that an image is recorded to a recording material (hereinafter referred to as a sheet) such as a sheet of paper, a plastic thin plate on the basis of image information.
Here, such a recorder is divided into a serial type using a serial scan system for performing a main scanning operation in a direction crossing a conveying direction (sub-scanning direction) of the sheet, and a line type in which the image is recorded by only the sub-scan in the conveying direction of the sheet.
In the recorder of the serial type, the image is recorded (mainly scanned) by recording means mounted on a carriage which can move along the sheet. After the image is completely recorded on one line, the sheet is fed (pitch conveyance) by a predetermined amount. Thereafter, an image on the next line is recorded (mainly scanned) with respect to the sheet again stopped. Such an operation is repeated so that the recording operation of the entire sheet is performed.
In the recorder of the line type, the sheet is set to a predetermined recording position and the recording operation on one line is collectively performed. Thereafter, the sheet is fed (pitch conveyance) by a predetermined amount, and the recording operation on the next line is further collectively performed. Such an operation is repeated so that the recording operation of the entire sheet is performed.
There are an ink jet system, a wire dot system, a thermal system, a laser beam system, etc. as a recording system of such a recorder. When the ink jet system for performing the recording operation by discharging ink from the recording means (recording head) to the sheet by utilizing thermal energy is used, the recording means is easily made compact and a high definition image can be recorded at high speed.
Further, running cost is inexpensive and noises are small since the ink jet system is a non-impact system. Furthermore, it is easy to record a color image by using ink of many colors. Especially, in the case of a line type using the recording means of the line type in which many discharging ports are arranged in a sheet width direction, the recording operation can be performed at higher speed.
Further, the recording means (recording head) with a structure having a liquid path arrangement (discharging port arrangement) of high density can be easily manufactured by using an electrothermal converting member, an electrode, a liquid path wall, a top plate, etc., which are formed on a substrate, through semiconductor manufacturing processes of etching, evaporation, sputtering, etc. so that the recorder can be made further compact. Furthermore, the recording means is easily elongated and sheet-shaped (two-dimensionally constructed), and is fully multiplied and mounted at high density by practically using the advantages of an IC technique and a micro processing technique.
For example, as described in Japanese Patent Application Laid-Open No. 56-148585, coated paper is often used as a sheet for coping with coloring, an improvement in image quality and an increase in operating speed of such a recorder. In the coated paper, an ink receiving layer is formed on basic paper having an ink absorbing property by using a porous inorganic pigment.
In the coated paper having such an ink receiving layer, it is possible to obtain a clear image with high image density and high resolution, and sufficiently cope with an increase in speed of a print output. For example, silica disclosed in Japanese Patent Application Laid-Open No. 56-185690 is used as the porous inorganic pigment for forming such an ink receiving layer, and has an excellent coloring property.
In the recorder using such an ink jet system, the sheet fed by feeding means is held by a platen in a recording region, and an image is recorded to the sheet by the recording head. Thereafter, the sheet is discharged by a sheet discharging apparatus arranged downstream of the recording head in the conveying direction.
Here, as this sheet discharging apparatus, there is one having a structure constructed of a sheet discharging roller and a spur arranged opposite to the sheet discharging roller and rotated by a rotation of the sheet discharging roller while the spur is pressed against the sheet. FIG. 9 is a view showing an attaching state of the spur constituting such a sheet discharging apparatus. A plurality of sharp projections 1a for reducing a contact area with the sheet are formed into serration on an outer circumference of this spur 1. The projections 1a come in contact with the sheet in this way, and the contact area with the sheet is reduced so that indentation onto the sheet on which unfixed ink is deposited just after printing, and an ink mark are restrained.
The spur 1 is attached to a base member 3 such that the spur 1 is rotated with an elastic shaft 2 as a center, and obtains pressing force against the sheet by the elastic shaft 2. Further, the spur 1 is regulated by thrust regulating walls 3a, 3b, 3c, 3d of the base member 3 such that a rotating direction of the spur 1 is in conformity with a discharging direction A of the sheet.
However, in such a conventional sheet discharging apparatus, there is a case in which the thrust regulating walls 3a, 3b, 3c, 3d of the base member 3 are slantingly deviated from the discharging direction A of the sheet so that the rotating direction of the spur 1 and the sheet discharging direction A are deviated from each other by an angle xcex8 as shown in FIG. 10. There is also a case in which a projecting portion 3e is formed by a burr, indentation, etc. in the thrust regulating wall 3c as shown in FIG. 11. In other words, there is a case in which no rotating direction of the spur 1 is perfectly in conformity with the sheet discharging direction A by shape deformation or skew feed of the sheet, etc. due to an accuracy in parts and a change in environment.
When no rotating direction of the spur 1 is perfectly in conformity with the sheet discharging direction A, a tip of one projection 1a of the spur 1 is deviated in a direction perpendicular to the sheet discharging direction A until the tip of one projection 1a of the spur 1 is separated from a printing surface of the sheet after this tip comes in contact with the printing surface. Therefore, when the coated paper having a soft surface layer is particularly printed, there is a case in which the ink receiving layer on the surface is separated and a spur trace is caused in a white dot shape on a printing surface.
In consideration of such a situation, an object of the present invention is to provide a sheet discharging apparatus and an image forming apparatus having the sheet discharging apparatus in which a sheet can be discharged without causing any spur trace on a surface of the sheet.
According to the present invention, there is provided a sheet discharging apparatus for discharging a sheet having an image formed thereon to a sheet discharging section, the apparatus comprising: sheet discharging means for discharging the sheet to the sheet discharging section; a rotary member having a plurality of projections formed on an outer circumferential portion thereof, the rotary member being rotated by a rotation of the sheet discharging means while pressing the sheet by the projections; and attitude changing means that changes an orientation of the rotary member in accordance with a movement of the sheet so that, when the rotary member is rotated while pressing the sheet, a rotating direction of the rotary member is in conformity with a discharging direction of the sheet.
Further according to the present invention, there is provided a sheet discharging apparatus, wherein the attitude changing means includes a retaining member for oscillatably retaining the rotary member, and regulating members, which are opposingly arranged on both sides of the rotary member while abutting against the rotary member, for regulating an axial movement of the rotary member, and wherein the regulating members are constructed in such a manner that the regulating members abut against the rotary member upstream of a contact point of the rotary member with the sheet in the sheet discharging direction so that an oscillation center of the rotary member is located upstream of the contact in the sheet discharging direction.
Still further, according to the present invention, there is provided a sheet discharging apparatus, wherein a distance between the regulating members opposingly arranged is gradually increased from an upstream side to a downstream side in the sheet discharging direction so that the oscillation center of the rotary member is located upstream of the contact point in the sheet discharging direction.
Yet further, according to the present invention, there is provided a sheet discharging apparatus, wherein projecting portions abutting against the rotary member are provided on the opposed regulating members upstream of the contact point in the sheet discharging direction so that the oscillation center of the rotary member is located on the upstream side in the sheet discharging direction from the contact point.
Yet still further, according to the present invention, there is provided a sheet discharging apparatus, wherein the distance between the regulating members opposingly arranged on the upstream side of the contact point in the sheet discharging direction is narrowed in comparison with the distance on the downstream side so that the oscillation center of the rotary member is located upstream of the contact point in the sheet discharging direction.
Further, according to the present invention, there is provided a sheet discharging apparatus, wherein the rotary member is rotated about an elastic shaft as a center, and is oscillatably retained by the retaining member through the elastic shaft.
Still further, according to the present invention, there is provided a sheet discharging apparatus, wherein the attitude changing means includes an oscillation member for rotatably retaining the rotary member, a retaining member for oscillatably retaining the oscillation member, and regulating members, which are opposingly arranged on both sides of the oscillation member while abutting against the oscillation member, for regulating an axial movement of the oscillation member; and wherein the regulating members are constructed in such a manner that the regulating members abut against the oscillation member upstream of a contact point of the rotary member with the sheet in the sheet discharging direction so that an oscillation center of the oscillation member is located upstream of the contact point in the sheet discharging direction.
Yet further, according to the present invention, there is provided a sheet discharging apparatus for discharging a sheet having an image formed thereon to a sheet discharging section, the apparatus comprising: sheet discharging means for discharging the sheet to the sheet discharging section; a rotary member having a plurality of projections formed on an outer circumferential portion thereof, the rotary member being rotated by a rotation of the sheet discharging means while pressing the sheet by the projections; and supporting means for supporting the rotary member so that, when the rotary member is rotated while pressing the sheet, an orientation of the rotary member is changed in accordance with a moving direction of the sheet.
Yet still further, according to the present invention, there is provided an image forming apparatus comprising an image forming section and a sheet discharging apparatus for discharging a sheet having an image formed in the image forming section to a sheet discharging section, the sheet discharging apparatus comprising one as set forth in any one of the above apparatus.
Furthermore, according to the present invention, a sheet having an image formed thereon is discharged to a sheet discharging section by sheet discharging means and a rotary member having a plurality of projections formed on an outer circumferential portion of the rotary member, the rotary member being rotated by a rotation of the sheet discharging means while pressing the sheet. When the rotary member is rotated while pressing the sheet, an orientation of the rotary member is changed by attitude changing means in accordance with a movement of the sheet so that the rotating direction of the rotary member is made coincide with a discharging direction of the sheet.